In the building industry it is often necessary to inspect the quality of a building construction. At the same time it may also be useful to inspect the quality of the construction during its phase of being built as well as after completion of the building work. Such an inspection, in particular with tunnels and bridges, is obligatory.
It is known to test building constructions by way of methods which are based on sound. Counted amongst these are the ultrasonic measurement method and the impact echo method. These methods are for example applied for determining the thickness of concrete parts, for localizing prestressing cuts and for locating defect locations. Both methods may be used individually and independently, or in combination, for recording readings. The basis of the methods is the examination of the running time and frequency behavior of the longitudinal waves at various measurement points of the object to be examined.
The quality of a building construction is inspected in that readings are recorded at various points of the building construction by way of test probes, which for example are based on the ultrasound method or on the impact echo method. One obtains information as to how the quality of the building construction is to be assessed on the basis of the recorded readings.
However one only obtains the readings for the locations at which a measurement is carried out. With an extensive building construction therefore measurements need to be carried out at many different locations. For this reason it is usual to introduce [modular] grids for the purpose of systemizing the measurement. Readings are recorded by measurements at the individual points of the grid. The measurement effort is reduced by way of this, whilst simultaneously ensuring that the building construction has been inspected in a manner covering its surface.
For inspecting a building construction, a test probe is placed at the locations of the building construction which are characterized by grid, and the readings are recorded at this location.
These measurements may be carried out manually. However the operation of the measurement apparatus changes on account of the fatigue of the personnel, which may considerably compromise the measurement accuracy. Inspections of an extensive area as a rule demand a large number of individual measurements. These then are particularly susceptible to the influences of operation.
In order to automize the measurement method at least partly, it is known to lay rails along a line of grid points, on which a measurement device is guided. The measurement device moves, usually automatically, to the individual grid points which are selected by the guiding of the rails, and records readings at these individual grid points by way of a test probe. In this manner one may automatically record a high number of readings along a line, and operating influences on the part of the personnel are almost completely ruled out.
This type of measurement however entails a considerable expense. Before a measurement may be carried out, firstly the rails must be laid along the line on which one would like to scan (cover in a grid-like manner) the object. The rails must be fixed in order to ensure a secure and exact guiding of the measurement device. Since usually several lines need to be scanned, which for example would be the case with the inspection of a large surface, the rails must be disassembled and re-laid. This procedure may furthermore be repeated quite often.